I use diff -Naur -X dontdiff oldtree newtree from my main kernel directory. (dontdiff attached)

Mark hasn't complained, although I think he does something different. As for compilation, I'm not aware of any method to make Make more efficient. It's entire purpose in life is to ensure that necessary files, but only necessary files get compiled. I can't see how you can ask it to do the former without allowing it to check all the potential dependancies.

Look on the bright side, only the first compilation takes a reallly long time.